In order to respond to the challenges of the broadband technology, and to meet requirements of new services, the third generation partner project (3GPP) puts forwards the standard work of long term evolution (LTE) plan, that is LTE technology, based on a dozen years of research of the beyond 3G technology. LTE adopts Frequency Division Multiple Access (OFDM/FDMA) instead of Code Division Multiple Access (CDMA) technology in the air interface, and extensively uses the multiple-input multiple-output (MIMO) technology and self-adaptive technology to improve the system throughput and system performance; in terms of the network architecture, LTE cancels radio network control (RNC) nodes used in the UMTS standard for a long time, and replaces them with a new flat architecture. It is believed that the 3GPP standard should maintain a competitive advantage to other radio communication standards for a relative long time by means of the LTE technology.
An initial cell search process is a key physical process for user equipment (UE) to establish a communication link with a base station in a cellular radio system, and the main purpose is to let the user equipment capture the time of the cell and synchronize with the frequency, and recognize the identification number of the local cell as well as some basic information of the cell broadcast at the same time. The basic step of the initial cell search process in a LTE system comprises: 1) UE performs a cell search in the center frequency band of the receiving band, and obtains a timing as well as cell identification information according to the Synchronization CHannel (SCH); 2) broadcast channel (BCH) information is detected based on the timing information maintained by the SCH with the base station, so as to obtain other configuration information of the cell; 3) and then UE receives and transmits data in the allocated frequency band according to the obtained broadcast control information. For the SCH signal detection, the LTE system adopts a hierarchical synchronization search mechanism, namely, a primary synchronization channel (P-SCH) and Secondary Synchronization Channel (S-SCH). Synchronization signal of the primary synchronization channel adopts three kinds of Zadoff-Chu (ZC) sequences in the frequency domain, mainly to identify the group identification number or sector number of the cell, and to perform frequency synchronization as well as 5 ms timing synchronization. At the same time, the primary synchronization signal is also taken as a pilot sequence for channel estimation when the secondary synchronization channel performs coherent detection; while the synchronization signal of the secondary synchronization channel is formed by making two short binary sequences interwoven and mapped, and the main function thereof is detecting the group identification number of the cell and synchronizing the frame timing. The UE obtains the cell number by detecting the synchronization channel, so as to acquire a reference signal in the system, and then performs coherent detection and decoding for the broadcasting channel, so as to obtain the broadcast information of the cell at last. The P-SCH and S-SCH adopts a Time Division Multiplexing mode, which transmits a radio frame twice per 10 ms. For the P-SCH, the same sequence is transmitted for the adjacent twice of transmission to implement 5 ms timing; for the S-SCH, the different sequences are transmitted for the adjacent twice of transmission to implement a radio frame timing synchronization of 10 ms. Synchronization channel occupies 62 subcarriers of the center except direct current subcarrier, and there are 5 virtual subcarriers respectively on both sides as protection bands. The broadcast information is mapped into the first subframe of each radio frame by means of encoding, rate matching, scrambling and modulation. The transmission cycle of the broadcast signal is 40 ms, the physical channel occupies 72 subcarriers except the direct current subcarrier, and the system bandwidth is 1.08 MHz. Since the synchronization channel and the broadcast channel are located on the 72 subcarriers of the center of the frequency domain, the UE is not required to have prior information of the system bandwidth during the initial cell searching.
The frequency domain signal sequence of the primary synchronization channel in LTE system, namely the primary synchronization sequence, is ZC sequence, and is expressed as:
                                          d            u                    ⁡                      (            n            )                          =                  {                                                                      ⅇ                                                            -                      j                                        ⁢                                                                                  ⁢                    π                    ⁢                                                                  un                        ⁡                                                  (                                                      n                            +                            1                                                    )                                                                    63                                                                                                                                        n                    =                    0                                    ,                  1                  ,                  …                  ⁢                                                                          ,                  30                                                                                                      ⅇ                                                            -                      j                                        ⁢                                                                                  ⁢                    π                    ⁢                                                                                            u                          ⁡                                                      (                                                          n                              +                              1                                                        )                                                                          ⁢                                                  (                                                      n                            +                            2                                                    )                                                                    63                                                                                                                                        n                    =                    31                                    ,                  32                  ,                  …                  ⁢                                                                          ,                  61                                                                                        Formula        ⁢                                  ⁢        1            
Wherein, the ZC root sequence indexes of u=25, 29, 34 represent the cell sector number of NID(2)=0, 1, 2 respectively. The primary synchronization is mapped into 62 low-frequency subcarriers except the one of k=0, that is, k=−31,−30, . . . −1,1, . . . , 30,31, and there are 5 subcarriers before and after them without transmitting any signals.
The classic primary synchronization signal detection method is adopting a time domain detection algorithm, that is, the local primary synchronization signal sequence index, namely the sector number of the local cell, transmitted by the base station side is determined by performing a matched filtering between the received signal and the local primary synchronization signal sequence, and by detecting the output amplitude of the matched filter.
The local primary synchronization sequence is generated by performing 64-point IFFT (Inverse Fast Fourier Transform) on the sequences of 62 subcarriers other than the direct current subcarrier, which are mapped onto the central frequency band, into the time domain during the traditional primary synchronization signal detection; and the generation method can be expressed as the following formula:
                                                                                                              x                    u                                    ⁡                                      (                    n                    )                                                  =                                                      1                                          64                                                        ⁢                                                            ∑                                                                        k                          =                                                      -                            31                                                                          ,                                                  k                          ≠                          0                                                                    31                                        ⁢                                                                                            d                          u                                                ⁡                                                  (                                                      k                            +                            31                                                    )                                                                    ·                                              ⅇ                                                  j                          ⁢                                                                                                          ⁢                          2                          ⁢                                                                                                          ⁢                          π                          ⁢                                                      nk                            64                                                                                                                                                          ,                                                                                          =                                  n                  =                  0                                            ,              1              ,              …              ⁢                                                          ,              63                                                                                          =                                                      1                                          64                                                        ⁢                                                            ∑                                                                        k                          =                                                      -                            31                                                                          ,                                                  k                          ≠                          0                                                                    31                                        ⁢                                                                  ⅇ                                                                              -                            j                                                    ⁢                                                                                                          ⁢                          π                          ⁢                                                                                                                    u                                ⁡                                                                  (                                                                      k                                    +                                    31                                                                    )                                                                                            ⁢                                                              (                                                                  k                                  +                                  32                                                                )                                                                                      63                                                                                              ·                                              ⅇ                                                  j                          ⁢                                                                                                          ⁢                          2                          ⁢                                                                                                          ⁢                          π                          ⁢                                                      nk                            64                                                                                                                                                          ,                                                                                          =                                  n                  =                  0                                            ,              1              ,              …              ⁢                                                          ,              63                                                          Formula        ⁢                                  ⁢        2            
Wherein,
                    d        u            ⁡              (        k        )              =          ⅇ                        -          j                ⁢                                  ⁢        π        ⁢                                  ⁢        u        ⁢                              k            ⁡                          (                              k                +                1                            )                                63                      ,k=0, 1, . . . , 62, that is a ZC sequence whose root sequence number is u, and whose sequence length is NZC=63.
However, the storage overhead of the local registers is found too much during the primary synchronization signal detection.